German Publication No. 2 301 186 discloses a load test apparatus provided with strain gages measuring the bending stress of a crane beam as the actual value indicator. In this load test apparatus, the strain gages are located above and below a cross piece connecting two plates. The bending stress of the crane beam is transmitted from the plates to the cross piece, and is determined by the strain gages as deflection. This known actual value indicator is difficult to manufacture, and allows for an abundance of erroneous test results. Also, great expenditures are required to surround this apparatus with a sealed housing in the area of the strain gages, protecting the latter from moisture and damage.
It has also been attempted to utilize diaphram gages for hoisting units, which will, for example, close a break contact when the compression spring in the gage is compressed by a certain degree under the effect of the load. The disadvantage of such diaphragm gages is their relatively great requirement for space, and expenditure in manufacturing.